Brand owners, designers and printers are beginning to request package printing with additional sensory features, for example, tactile effects, to add a feeling of increased value to their products. In addition, as a result of worldwide counterfeiting and piracy, security is now a crucial element of some packaging. Package security features are becoming more desirable or necessary to protect brand owners from financial losses associated with product and brand counterfeiting. The cost of product counterfeiting is an estimated $500 billion each year. By adding non-reproducible printed effects to packaging, it is possible to both provide security features as well as differentiation from other similar products, which allows for a potential point-of-purchase advertising tool.
Fluorescent inks and toners are among the most widely used security printing features. A printed document is usually authenticated by detecting the light emitted by the fluorescent component when subjected to black light. The light emitting property cannot be reproduced in a second generation copy. The fluorescent inks and toners are generally applied with ink-jetting systems.
Ink-jetting printing systems are known in the art, and thus extensive description of such devices is not required herein. Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term- storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Hot-melt inks typically used with ink-jet printers have a wax-based ink vehicle, e.g., a crystalline wax. Such solid ink-jet inks provide vivid color images. In typical systems, the crystalline-wax inks are jetted onto a transfer member, for example, an aluminum drum, at temperatures of approximately 130-140° C. The wax-based inks are heated to such high temperatures to decrease their viscosity for efficient and proper jetting onto the transfer member. The transfer member is at approximately 60° C., so that the wax will cool sufficiently to solidify or crystallize. As the transfer member rolls over the recording medium, e.g., paper, the image comprised of wax-based ink is pressed into the paper.
However, the use of crystalline waxes places limitations on the printing process. First, dye diffusion from the ink into paper or other substrates (will lead to poor image quality and showthrough), and the ability for the dye to leach into another solvent that makes contact with the image (will lead to poor water-/solvent-fastness). Dye diffusion is undesirable in many circumstances; its reduction or absence in the image leads to loss of visual or security effect. The presence of the extracted dye on other surfaces or in food stuffs is most undesirable. Furthermore, increased mechanical robustness is desired.
While such known ink compositions are used successfully, a need remains for improved phase-change ink compositions suitable for hot-melt ink-jet printing processes. There is still a need for ink compositions that can be processed at lower temperatures and with lower energy consumption, that have improved robustness, and that have improved jetting reliability and latitude with respect to meeting both the jetting and transfuse requirements of curable ink compositions. In addition, a need remains for phase-change ink compositions that exhibit desirably low viscosity values at jetting temperatures, that generate images with improved look and feel characteristics, that generate images with improved hardness and toughness characteristics, and that are suitable a number of commonly used packaging substrates.
Furthermore, it is desirable to ensure, to the extent that toxic or otherwise hazardous compounds are used in such products, that migration, evaporation or extraction of such materials from the cured material is controlled or ameliorated. When used in certain applications, for example food packaging, and direct to paper printing, it is desirable to reduce the amount of or eliminate altogether extractable species present, for example to meet environmental, health and safety requirements,
A particular source of contamination in UV/visible light-cured products has been identified as residual unreacted monomers and photoinitiators and their decomposition products, such as benzaldehydes. Consequently, most commercially available photoinitiators are prohibited from use in such applications, examples of which include foil-laminating adhesives for food packaging, coil coatings for kitchen appliances and certain drug delivery/packaging systems. Similar issues are known to exist when unbound fluorescent particles are added to food packaging systems.
While known compositions and processes are suitable for their intended purposes, a need remains for improved ink incorporating non-migratable, fluorescent molecules for providing both security features as well as differentiation from other similar products in food packaging applications. In addition, a need remains for improved phase change inks. Further, a need remains for fluorescent molecules that are soluble in, miscible in, or otherwise compatible with phase change ink vehicles. Further, there is a need for fluorescent molecules that exhibit reduced migration through cured images when used in curable phase change inks. Additionally, there is a need for fluorescent molecules having improved affinity for phase change inks exhibiting a gel phase during the printing process. A need also remains for fluorescent molecules having reduced volatility. Further, a need remains for fluorescent molecules that have improved affinity for the ordered microstructure of the gel phase, as opposed to being excluded from that order. Additionally, a need remains for fluorescent molecules that are highly curable. There further remains a need for phase change inks with reduced or eliminated amounts of post fusing extractable species.